Anti-resonant Reflecting Optical Waveguides (ARROW) have several advantages over other types of waveguides. They can be formed upon silicon, using relatively thin layers compared to other waveguides, for easier compatibility with other electronic integrated circuits. At the same time, they can have a large mode for coupling to optical fibers. Additionally, they are relatively easy to manufacture, as they require no exotic materials.
These waveguides typically consist of a layer of silicon oxide built upon a silicon substrate. An interference layer of silicon is then placed upon the first layer of silicon oxide, followed by another layer of silicon oxide. All of these materials can be deposited with relative ease. The silicon layer sandwiched between the two silicon oxide layers functions as a passive interference cladding layer. The thickness of the interference layer is not critical.
Vertical coupling has been achieved in such layered structures made of semiconductor materials by the use of periodic gratings in the materials that make up the structure. This technique can be used to couple light between the top core layer and the interference layer.
Active optical modulators are normally difficult to produce in or on silicon. Silicon exhibits no linear electro-optic effect, although changes in absorption or refractive index may be induced by modulating the density of free carriers. All-silicon waveguides tend to have a high propagation loss due to these same free-carrier effects and are difficult to fabricate to have a high modulation efficiency, because of poor modal overlap. All-dielectric waveguides can have low loss, but are typically passive and not useful for modulation. Using an ARROW structure in conjunction with vertical coupling will make it possible to combine the low-loss propagation of dielectric waveguides with the capability of modulating or switching light using free-carrier effects.